Complementary and Regioselective Synthesis of Isomeric 3-[Isoxazol-3(or 5)-yl]indoles from β-Ethylthio-β-indolyl-α,β-unsaturated Ketones

A simple and efficient method for the complementary and regioselective synthesis of isomeric 3-(isoxazol-5-yl)indoles and 3-(isoxazol-3-yl)indoles has been developed by the regioselective cyclocondensation reaction of β-ethylthio-β-indolyl-α,β-unsaturated ketones and hydroxylamine hydrochloride. It was found that the cyclocondensation reaction in the presence of excess NaOEt in refluxing EtOH gives 3-(isoxazol-5-yl)indoles in good yields, whereas using NaOAc in boiling AcOH gives 3-(isoxazol-3-yl)indoles in good yields.